OBJECTIVE: To understand the control of transcription during infection of the cotton bollworm (Heliothis zea) by a nuclear polyhedrosis virus. APPROACH: DNA from the virus will be purified and characterized as to its size, density and conformation. Ultracentrifugation and electron microscopic techniques will be employed. Then, RNA polymerase will be purified from the bollworm and separated into its various isozymes. These will be identified by their salt optima, divalent cation requirements, template preferences and sensitivity to the inhibitor alpha-amanitin. The central part of this study will involve an investigation of the activity of purified bollworm RNA polymerase with viral DNA as template. Factors which stimulate this activity will be sought in fractions from the various purification steps. If such stimulatory (sigma-like) factors are found, their specificities will be investigated. This will involve distinguishing classes of RNA transcripts during virus infection. Our starting point will be to distinguish early from late transcription (pre- and post-DNA replication). Then, hybridization-competition studies will reveal whether the bollworm factor(s) stimulate(s) early or late transcription, or, if no stimulatory factor is found, whether the bollworm polymerase itself transcribes early or late genes or both. Special attention will focus on the transcription of the m-RNA for the major viral product, the polyhedral protein. We will attempt to purify this m-RNA from infected, cultured bollworm cells and to answer the following questions. It is an early or late transcript? Does bollworm polymerase, in the presence or absence of any sigma-factor, transcribe this gene? If bollworm polymerase, even with bollworm factor, cannot transcribe this gene, we will seek a viral-specified factor in infected bollworms or infected bollworm cells grown in culture.